抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Unlike other methods for docking ligands to the rigid 3D structure of a known protein receptor, Glide approximates a complete systematic search of the conformational, orientational, and positional space of the docked ligand In this search, an initial rough positioning and scoring phase that dramatically narrows the search space is followed by torsionally flexible energy optimization on an OPLS-AA nonbonded potential grid for a few hundred surviving candidate poses The very best candidates are further refined via a Monte Carlo sampling of pose conformation; in some cases, this is crucial to obtaining an accurate docked pose Selection of the best docked pose uses a model energy function that combines empirical and force-field-based terms Docking accuracy is assessed by redocking ligands from 282 cocrystallized PDB complexes starting from conformationally optimized ligand geometries that bear no memory of the correctly docked pose Errors in geometry for the top-ranked pose are less than 1 A in nearly ha

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Glide: a new approach for rapid, accurate docking and scoring. 1. Method and assessment of docking accuracy.

Use of bacteriophage T7 RNA polymerase to direct selective high-level expression of cloned genes

A novel scoring function to estimate protein-ligand binding affinities has been developed and implemented as the Glide 4.0 XP scoring function and docking protocol. In addition to unique water desolvation energy terms, protein-ligand structural motifs leading to enhanced binding affinity are included: (1) hydrophobic enclosure where groups of lipophilic ligand atoms are enclosed on opposite faces by lipophilic protein atoms, (2) neutral-neutral single or correlated hydrogen bonds in a hydrophobically enclosed environment, and (3) five categories of charged-charged hydrogen bonds. The XP scoring function and docking protocol have been developed to reproduce experimental binding affinities for a set of 198 complexes (RMSDs of 2.26 and 1.73 kcal/mol over all and well-docked ligands, respectively) and to yield quality enrichments for a set of fifteen screens of pharmaceutical importance. Enrichment results demonstrate the importance of the novel XP molecular recognition and water scoring in separating active and inactive ligands and avoiding false positives.

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Extra Precision Glide: Docking and Scoring Incorporating a Model of Hydrophobic Enclosure for Protein-Ligand Complexes

Networks of interacting biomolecules carry out many essential functions in living cells, but the 'design principles' underlying the functioning of such intracellular networks remain poorly understood, despite intensive efforts including quantitative analysis of relatively simple systems Here we present a complementary approach to this problem: the design and construction of a synthetic network to implement a particular function We used three transcriptional repressor systems that are not part of any natural biological clock to build an oscillating network, termed the repressilator, in Escherichia coli The network periodically induces the synthesis of green fluorescent protein as a readout of its state in individual cells The resulting oscillations, with typical periods of hours, are slower than the cell-division cycle, so the state of the oscillator has to be transmitted from generation to generation This artificial clock displays noisy behaviour, possibly because of stochastic fluctuations of its components Such 'rational network design may lead both to the engineering of new cellular behaviours and to an improved understanding of naturally occurring networks

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A synthetic oscillatory network of transcriptional regulators

The degQ and degS genes of Escherichia coli encode proteins of 455 and 355 residues, respectively, which are homologs of the DegP protease. The purified DegQ protein has the properties of a serine endoprotease and is processed by the removal of a 27-residue amino-terminal signal sequence. A plasmid expressing degQ rescues the temperature-sensitive phenotype of a strain bearing the degP41 deletion, implying that DegQ, like DegP, functions as a periplasmic protease in vivo. Deletions in the degQ gene cause no obvious growth defect, while those in the degS gene result in a small-colony phenotype. The latter phenotype is rescued by a plasmid expressing the degS gene but not by plasmids expressing the degQ or degP genes. This result and the inability of a plasmid expressing degS to rescue the temperature-sensitive degP41 phenotype indicate that the DegS protein is functionally different from the DegQ and DegP proteins.

Characterization of degQ and degS, Escherichia coli genes encoding homologs of the DegP protease.

In Gram-negative bacteria, outer-membrane integrity is essential for survival and is monitored by the σ(E) stress-response system, which initiates damage-repair pathways. One activating signal is unassembled outer-membrane proteins. Using biochemical and genetic experiments in Escherichia coli, we found that off-pathway intermediates in lipopolysaccharide transport and assembly provided an additional required signal. These distinct signals, arising from disruptions in the transport and assembly of the major outer-membrane components, jointly determined the rate of proteolytic destruction of a negative regulator of the σ(E) transcription factor, thereby modulating the expression of stress-response genes. This dual-signal system permits a rapid response to dysfunction in outer-membrane biogenesis, while buffering responses to transient fluctuations in individual components, and may represent a broad strategy for bacteria to monitor their interface with the environment.

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Dual Molecular Signals Mediate the Bacterial Response to Outer-Membrane Stress

It is rare for amino-acid substitutions on the surface of proteins to have large stabilizing or destabilizing effects. Nevertheless, one substitution of this type, the Tyr 26----Cys mutation in lambda Cro, increases the melting temperature of the protein by 11 degrees C and the stability by 2.2 kcal mol-1. Here we show that the stability of Cro can be increased by many different amino-acid substitutions at position 26, with increasing stability showing a good correlation with decreasing side-chain hydrophobicity. As Tyr 26 is hyper-exposed to solvent in the Cro crystal structure, we suggest that wild-type and variant proteins with other hydrophobic side chains at position 26 are destabilized as a result of a reverse hydrophobic effect caused by the side chain being more exposed to solvent in the native than in the denatured state.

Reverse hydrophobic effects relieved by amino-acid substitutions at a protein surface

Proline Residues at the C Terminus of Nascent Chains Induce SsrA Tagging during Translation Termination

In the ClpXP compartmental protease, ring hexamers of the AAA(+) ClpX ATPase bind, denature and then translocate protein substrates into the degradation chamber of the double-ring ClpP(14) peptidase. A key question is the extent to which functional communication between ClpX and ClpP occurs and is regulated during substrate processing. Here, we show that ClpX-ClpP affinity varies with the protein-processing task of ClpX and with the catalytic engagement of the active sites of ClpP. Functional communication between symmetry-mismatched ClpXP rings depends on the ATPase activity of ClpX and seems to be transmitted through structural changes in its IGF loops, which contact ClpP. A conserved arginine in the sensor II helix of ClpX links the nucleotide state of ClpX to the binding of ClpP and protein substrates. A simple model explains the observed relationships between ATP binding, ATP hydrolysis and functional interactions between ClpX, protein substrates and ClpP.

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Robert T. Sauer

Papers

Characterization of degQ and degS, Escherichia coli genes encoding homologs of the DegP protease.

Dual Molecular Signals Mediate the Bacterial Response to Outer-Membrane Stress

Reverse hydrophobic effects relieved by amino-acid substitutions at a protein surface

Proline Residues at the C Terminus of Nascent Chains Induce SsrA Tagging during Translation Termination

Communication between ClpX and ClpP during substrate processing and degradation